The present invention relates to a cable coupling for automatically coupling through electrical heating and/or control current lines, particularly between track-bound vehicles, wherein during or after the mechanical coupling together of the vehicles, mutual contact between contact boxes containing pressure or plug-in contacts mounted in contact carriers causes these contacts to come into engagement and wherein, in addition to coupling the electrical lines, light-conductors must also be coupled in for the optical transmission of instructions or other information.
The periodical "ZEV, Glasers Annalen" [Glass Makers' Annual] 103 (1979) No. 2/3, February/March, pages 114-124, discloses the coupling of light conductive fibers together with electric current lines when automatically coupling electrical cables for trains. Control information is then transmitted from car to car by means of the light-conductive fibers. The light-conductive fibers are coupled together by means of a plug-in connection in which the highly polished fiber ends abut on one another in a precisely centered manner.
For so-called fixed optical conductor couplings there no longer exist any problems regarding coupling with low attenuation. The fibers can be brought together in the plug-in and rotary couplings with very close tolerances, high precision and accuracy. However, with automatic cable couplings there exists the difficulty of adapting the plug-in connection to rough movements of the train and to be able to accurately guide the cable ends with the required close tolerances over a longer period of time without thereby causing excess wear and thus impairing the transmission quality.
The active part of an optical fiber has a diameter, for example, of 200.mu., and the threshold of the permissible center offset should be low. A very slight angular displacement is also permissible. These values can be achieved only with very close tolerances and with the use of fine centering means in the plug-in connections, which are far beyond the already high tolerance requirements for electrical couplings. Wear makes such plug-in connections very short-lived and manufacture becomes considerably more expensive.
Even more serious is the problem of soiling. A grain of dust can already completely eliminate light transmission because the grain is usually larger than the diameter of the fiber, or as the fiber ends are brought together such grain could scratch the highly polished frontal faces to such an extent that attenuation would take on untenable values. In the prior art cable coupling in which the ends of the light-conductive fibers are coupled directly, these problems are addressed as well. Centering is there effected by special guide pins and a mechanically susceptible slide structure is intended to take care of sealing and thus keep away the dust. But this gives rise to considerable drawbacks.